8028792: (ch) Channels native code needs to be checked for methods calling JNI with pending excepitons

[Alan Bateman]

This change updates the JNI usage in several native methods to handle 
exceptions that may potentially be pending after calls to FindClass and 
GetFieldID. It's primarily init methods called in static initializers 
that are updated.

Chris - I checked the SCTP implementation while in the area and there 
are a few updates (I can separate these into another bug if you wish).

Volker - I've taken the liberty of updating AixNativeDispatcher.c but I 
have no way to check the build. If you'd prefer then I can leave this 
out of this change. One other thing is that the native init method 
returns an int/jint but it probably can be void as that would match the 
other platforms.

The webrev with the proposed changes is here:

http://cr.openjdk.java.net/~alanb/8028792/webrev/

Thanks,
Alan.